1. Field of the Invention
The present invention relates to 1,4-bis-formyl cyclohexane polycarboxylic acids, to a process of producing same, and to compositions for and methods of using said acids for preventing scale-forming deposits.
2. Description of the Prior Art
It is known to employ polyphosphates and more recently phosphonic acids for preventing precipitation of alkaline earth metal ions. Two groups of phosphonic acids have proved to be especially effective for this purpose, namely the amino alkylene phosphonic acids such as, for instance, nitrilo tris-(methylene phosphonic acid) and the alkane diphosphonic acids such as, for instance, hydroxy ethane diphosphonic acid. The use of phosphonic acids is preferred over that of polyphosphates because the former are stable against hydrolysis and, therefore, fully retain their effectiveness in acid as well as alkaline media.
It is also known that when using the phosphonic acids, even amounts lower than the stoichiometrically required amounts are sufficient in order to retain in solution the hardness causing agents in water. This phenomenon is generally known as "threshold effect" or also as "seeding effect" (Ralston "Journal Petroleum Technology," vol. 21 (1969), pp. 1029 to 1036).
Because nitrogen and phosphorus containing compounds have been made responsible for the eutrophication of rivers and lakes, many attempts have been made to find new nitrogen- and phosphorus-free compounds having such threshold effectiveness.
Heretofore mainly two classes of compounds which contain neither nitrogen nor phosphorus and which are effective in amounts below the stoichiometrically required amounts have become known. Such compounds are, on the one hand, polymers of the most diverse composition (Elliot "Desalination," vol. 8 (1970), p. 232) and, on the other hand, modified polysaccharides, for instance, starches which have been degraded by acids or by oxidation (U.S. Pat. No. 3,791,978).
Both types of agents with threshold effectiveness, however, can be used only in higher concentrations than the phosphonic acids.
Furthermore, it is also known that the cyclohexane-1,2,3,4,5-pentacarboxylic acid has such an effectiveness (U.S. Pat. No. 3,784,469).